TechTalk8084 Service Bulletin/Repair Instructions

DT12 TRYING TO DOWN SHIFT
Joe Potts 16 posts since Mar 18, 2015

DT12 TRYING TO DOWN SHIFT Jan 26, 2021 8:49 PM

vin GH8806 2015 Cascadia back story we pulled trans because of internal speed sensor damaged. got a quote

for new trans to customer for what ever reason our parts guy quoted a Detroit trans and a Weller trans, saying

we could get the Weller faster. customer approved the Weller. we were given the wrong trans to begin with but

now have the right one. the first time we gave the truck back to the customer he was not happy with shifting.

I found while driving it shifts up fine all the way. but letting the truck slow down once it hits 9th gear it starts

freaking out neutral and 9th and neutral and 9th on and off until truck slows down enough to easily go into 8th.

this is with and without the engine brake on, also the hill start ad light flashes this entire freaking out time and

this is repeatable every time going down the gears. log file to Detroit they sayed they would be replacing the

trans if it was there trans , they denied any responsibility for Weller. we have pulled the trans ands shipped

it back to Weller and they went through the entire trans and shipped it back. we reinstalled the trans to have

the same problem exactly. does anyone have any clue why only down shifting from 9th is there some sort if

synchro ? trans ? tcm ? shift selector ? Weller is saying nothing is wrong with there reman and Detroit will not

help. im in that hard spot. why 9th gear only.
Talbert Simonian 1,881 posts since Nov 21, 2014

Re: DT12 TRYING TO DOWN SHIFT Jan 26, 2021 10:21 PM

Did you do a relearn?
Chaz Trimble 1,370 posts since Feb 2, 2015

Re: DT12 TRYING TO DOWN SHIFT Jan 27, 2021 12:25 AM

Wow I’m surprised weller is getting into dt12’s and I will definitely push to stay far far away from them. The dt12

is not anywhere near an Eaton for just anyone to be rebuilding them. Have you checked for any ABS issues?

Have you checked your split pin shifts? Have you monitored range shifts? Countershaft speed in normal ranges?

Requested and actual along with actual engine speed can tell a lot.
Jesse Gutierrez 496 posts since Mar 5, 2017

Re: DT12 TRYING TO DOWN SHIFT Jan 27, 2021 8:46 PM

I Just ran into a similar issue, what is the TCM software level? I had to call CSC they had a fix for erratic/

grinding when down shifting, updated my TCM and this corrected my problems
Scott Trippel 4,094 posts since Dec 13, 2014

Re: DT12 TRYING TO DOWN SHIFT Jan 27, 2021 8:51 PM

Can you post a log file?
1
DT12 TRYING TO DOWN SHIFT
Did you follow shift up or down symptom troublesooting?
Joe Potts 16 posts since Mar 18, 2015

Re: DT12 TRYING TO DOWN SHIFT Feb 15, 2021 5:25 PM

I did solve the problem the long way. customer was big enough to lone us a sister truck to do part swaps. we

started with donor tcm and shift controller on the weller in the problem truck and nothing changed. we then

pulled trans again and installed the donor trans and original tcm and shift controller, so only the weller was

isolated. truck now works just fine. weller ended up taking back there trans and giving us back a core and the

customer bought a Detroit trans. im not trying to bash weller but we were up a creek.
Jesse Gutierrez 496 posts since Mar 5, 2017

Re: DT12 TRYING TO DOWN SHIFT Feb 15, 2021 11:42 PM

Nice update and I have ran into Weller manual trans having issues from time to time. I also did not know

anyone was rebuilding DT-12 either . We sometimes have customer who buy them salvage or from junk yards

and they are a 50/50 gamble
2

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